18 ARKIV FÖR ZOOLOGI. BAND 7. N:0 2. 



tine, and cement) these teeth very nearly resemble as well 

 each other as at the same time normal mammalian teeth. 

 They liave thus only been altered with regard to tlieir shape 

 which has been simplified to a single conical fång (or spade- 

 like crown in Phoccena) at the same time as the double roots 

 have coalesced into one, which then has got the power of 

 growing longer. There cannot be spöken about reduction 

 neither of the enamel layer nor of the whole crown in the 

 teeth of these four species as justly has been done above 

 concerning the White whale. The teeth of the same four species 

 do not show any secondary growth of cement either w^hich 

 is so very important for the development of the teeth of the 

 White whale The conclusion pronounced above about the 

 independent development of the White whale on one and the 

 typical Dolphins and Porpoises on the other side is thus 

 fully supported by these investigations of the structure of 

 the teeth of the latter animals. 



In the same respect in w^hich the teeth Delphinapterus 

 differ from those of the Dolphins viz. in the strong develop- 

 ment of the surrounding coat of cement they offer a resem- 

 blance to the teeth of the Cachalot. The latter consist also of 

 a central cylinder of dentine and a surrounding very thick 

 layer of cement which constitutes the main bulk of the teeth. 

 This can easily be seen on any tooth of a Sperm whale which 

 is somewhat worn. Ås the White whale and the Cachalot 

 are so greatly different in many other respects this likeness 

 can only be explained as a product of analogous development. 

 In both cases the crowns of the teeth have become reduced 

 for some reason. When låter the teeth have been needed 

 the animals have for the further development of them only 

 had the roots to fall back upon w4th their central dentine 

 and surrounding cement. 



Tryckt den 5 juli 1910. 



Uppsala 1910. Almqvist & Wiksells Boktryckeri-A.-B. 



